Natriuretic peptide receptors in cultured rat diencephalon

To characterize the type of cell expressing natriuretic peptide receptors in the brain and the nature of these receptors, we conducted studies in primary cultured glial and neuronal cells derived from fetal rat diencephalon. The glial predominant cultures (95% of total cells and glial fibrillary acidic protein positive) expressed nearly a 10-fold greater specific binding of the natriuretic peptides to cell surface receptors compared with the neuron-predominant cultures. Scatchard analysis of binding studies with 125I-atrial natriuretic peptide (ANP) and 125I-brain natriuretic peptide (BNP) revealed a single class of receptors with dissimilar affinities (0.25 +/- 0.09 and 0.74 +/- 0.07 nM, respectively, n = 3 experiments p less than 0.01) but similar numbers of binding sites for both peptides (93 and 88 fmol/mg of protein, respectively). Cross-linking of 125I-ANP and BNP to cultured glia followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography identified distinct bands at either approximate Mr 130,000, or 102,000 and 66,000, corresponding to two high molecular weight (B) receptors and one low molecular weight (C) receptor described in other tissues. Different subtypes of astrocytes appeared to express different B receptors. Binding and cross-linking of radiolabeled ANP or BNP were competitively inhibited equally by unlabeled ANP or BNP, indicating that ANP and BNP probably bind the same receptors. The glial cultures functionally expressed a receptor(s) with guanylate cyclase activity; BNP was less potent than ANP in stimulating cGMP at lower concentrations. These results indicate that both high and low molecular weight natriuretic peptide receptors are expressed in astrocyte-predominant cultures from the fetal diencephalon and suggest that glia participate in several actions of ANP which are probably mediated through this area of the brain.